LECTURE 10.1LECTURE 10.1

LECTURE OUTLINELECTURE OUTLINE

Weekly DeadlinesWeekly DeadlinesElectronic Properties IElectronic Properties I

Name Properties 2: Electronic Properties

Lectures Lecture 10.1 Electronic Properties ILecture 10.2 Electronic Properties II

Required Book Reading 1(For the end-of-UNIT quiz)

Part E:Chapters 28, and 29.

Animations Electron Pump, GedankenExpIan Harrison: "EPropsF"BiographiesMineral of the Week

Assignments due this week Assignment 6, A Materials' Essay; Part IV, is dueWednesday midnight

Practice Quiz Practice quiz questions are available on ANGEL, in theLesson 10 folders.

End of Unit Quiz Quiz 10 will consist of ~ twenty (20) questions for a total offifty (50) points. Quizzes are “individualized”, but with thequestions taken from a large database.

Material covered: Book Reading and Animations

ELECTRONIC PROPERTIES IELECTRONIC PROPERTIES I

Metallic ConductionMetallic ConductionOhm’s lawOhm’s lawNumber of Free Electrons/AtomNumber of Free Electrons/AtomDrift VelocityDrift VelocityFree Electron/Electron Hole PairsFree Electron/Electron Hole PairsThe Group IV ElementsThe Group IV Elements

THE WATER ANALOGUE: CURRENT THE WATER ANALOGUE: CURRENT AND PRESSUREAND PRESSURE

THE ELECTRON PUMPTHE ELECTRON PUMP

CONDUCTIVITY AND OHM’S LAWCONDUCTIVITY AND OHM’S LAW

CONDUCTIVITY AND OHM’S CONDUCTIVITY AND OHM’S LAWLAW

The current that flows through a material is The current that flows through a material is proportional to the Voltage (or Electrical proportional to the Voltage (or Electrical Pressure Difference)Pressure Difference)

Or:Or:

I I V VOr:Or:

I = I = VVWhere Where is called the conductivity. is called the conductivity.

CONDUCTIVITY AND OHM’S CONDUCTIVITY AND OHM’S LAWLAW

The current that flows alongthe wire is equal to the numberof charge carriers (electrons)times their “drift velocity” times the charge on the electron

Or:

I = qnv

CONDUCTIVITIES OF CONDUCTIVITIES OF MATERIALSMATERIALS

For metals:For metals: n/atom ~ 1n/atom ~ 1 For non-metals:For non-metals: n/atom ~ 0n/atom ~ 0 For semiconductors:For semiconductors: n is small, but finiten is small, but finite For metals: the For metals: the

conductivity (s) depends conductivity (s) depends on how the drift velocity on how the drift velocity varies with e.g., varies with e.g., temperaturetemperature

HOW ARE FREE ELECTRONS CREATED IN A HOW ARE FREE ELECTRONS CREATED IN A COVALENTLY BONDED SEMICONDUCTOR?COVALENTLY BONDED SEMICONDUCTOR?

Free electron/electron hole pairs may be Free electron/electron hole pairs may be created by:created by:Light Light √√√√HeatHeat √√ √√Electric Field Electric Field xxxx

CREATION OF A FREE CREATION OF A FREE ELECTRON/ELECTRON-HOLE PAIRELECTRON/ELECTRON-HOLE PAIR

IONIZATION ENERGIES OF THE IONIZATION ENERGIES OF THE GROUP IV ELEMENTS IGROUP IV ELEMENTS I

For diamond-C, the outer-For diamond-C, the outer-shell electrons are in the L-shell electrons are in the L-shell. They are so closely shell. They are so closely bound, that the ionization bound, that the ionization energy is prohibitively high: energy is prohibitively high: diamond-C is a prototypical, diamond-C is a prototypical, electrical insulatorelectrical insulator

n/atom ~ 0n/atom ~ 0

IONIZATION ENERGIES OF THE IONIZATION ENERGIES OF THE GROUP IV ELEMENTS IIGROUP IV ELEMENTS II

For lead, the outer-shell For lead, the outer-shell electrons are in the P-shell. electrons are in the P-shell. They are so loosely bound, They are so loosely bound, that lead’s outer-shell that lead’s outer-shell electrons are free at room-electrons are free at room-temperatures: lead is a temperatures: lead is a prototypical, electrical prototypical, electrical conductorconductor

n/atom ~ 1n/atom ~ 1

IONIZATION ENERGIES OF THE IONIZATION ENERGIES OF THE GROUP IV ELEMENTS IIIGROUP IV ELEMENTS III

For silicon and For silicon and germanium, the ionization germanium, the ionization energies are such that energies are such that their electrical properties their electrical properties are midway between are midway between those of a “typical” those of a “typical” insulator, and a “typical” insulator, and a “typical” conductor: they are conductor: they are elemental elemental semiconductors!semiconductors!

ELECTRICAL CONDUCTIVITY ELECTRICAL CONDUCTIVITY IN A METALIN A METAL

THE DRIFT VELOCITY AND THE THE DRIFT VELOCITY AND THE CONDUCTIVITY OF METALSCONDUCTIVITY OF METALS

In metals, the variation in In metals, the variation in conductivity is related to the conductivity is related to the variation in the drift velocity of variation in the drift velocity of the electrons.the electrons.

The drift velocity decreases as The drift velocity decreases as the frequency of atomic the frequency of atomic collisions increases.collisions increases.

The drift velocity decreases as The drift velocity decreases as temperature increases.temperature increases.

The drift velocity decreases as The drift velocity decreases as the solute level increases.the solute level increases.

EFFECT OF “PURITY” AND TEMPERATURE EFFECT OF “PURITY” AND TEMPERATURE ON METALLIC CONDUCTIVITIESON METALLIC CONDUCTIVITIES